This project is based on our observation that glucocorticoids can initiate division of density-inhibited fibroblasts. Division of spontaneously-transformed and viral-transformed malignant fibroblasts is not stimulated, even if their growth rate is greatly slowed by placing them in medium containing low levels of serum. The goal of these studies is to analyze the involvement of previously identified surface membrane changes and glucocorticoid-specific components in the initiation of division of density-inhibited fibroblasts by cortisol. Levels of cortisol which initiate division bring about increased concanavalin A-specific agglutination of the cells. We plan to investigate the relationship of this cell surface change to the initiation of cell division. Since protease treatment of density- inhibited fibroblasts has been reported to also bring about increased concanavalin A agglutination and initiation of cell division, we will investigate the possibility that the cortisol effect is mediated by protease. We also plan to investigate some transport changes that have been implicated in the initiation of cell division by serum and by protease. Studies on other systems have shown that glucocorticoid-specific cell components and interactions among them appear to be involved in the action of the hormone. We plan to study their involvement in the initiation of cell division by glucocorticoids. A basic feature of our approach is to employ a series of our nonresponsive spontaneously- transformed lines. We anticipate that these "mutants" will have a series of altered glucocorticoid-specific components that account for their inability to respond to cortisol. We will assay for functional components in cell-free extracts of sensitive and nonresponsive cells using previously described binding assays.